The following projects are planned. (a) investigation of rhythmicity in sexual behavior of male rats and the physiological substrates; (b) effects of variations in photoperiod on male sexual behavior in rodents; (c) determine the circadian and infradian estradiol rhythms of the female rat in constant light; (d) study of the effects of variations in photoperiod on ovarian sensitivity in the female rat; (e) determination of the contribution of the adrenal cortex to the constant light-induced disruption of the female estrous cycle; (f) measurement of several physiological and behavioral rhythms of the female exposed to continuous light; (g) study of the effects of photoperiod reversal on the estrous cycle of the golden hamster; (h) effects of self-selection of environmental illumination on the estrous cycle of the golden hamster. BIBLIOGRAPHIC REFERENCES: Campbell, Constance S., Neena B. Schwartz and Marianne Gorski Firlit, The role of adrenal and ovarian steroids in the control of serum LH and FSH. Endocrinology, 1977. In press. Campbell, C.S. and Neena B. Schwartz, An overview of regulatory mechanisms in the rodent. Journal of toxicology and Environmental Health, 1977. In press.